This project will involve studies of the extracellular matrix and its changes with aging in rat cardiac muscle by means of a collaborative effort which will include structural, mechanical, and biochemical approaches. The specific aims are to: 1) improve antibody localization at the ultrastructural level in order to image both cell surface features and labelled antibodies; 2) localize on the myocyte surface elastin, collagen, micro-fibrillar protein, fibronectin and proteoglycan as a function of age; 3) determine the changes that occur in the structure of extracellular fibers (i.e., epimysial and perimysial collagen fibers, endomysial weave and strut fibers, and elastin) as a function of age in rats; 4) correlate changes in disposition and convolution of collagen and elastin fibers with mechanical properties of whole papillary muscles and length controlled segments of papillary muscles; 5) perform each of the above studies on tissue obtained from rats treated with lathyritic agents which block cross-linking in fibers; and 6) perform microscopy and antibody labeling microscopy to characterize extracellular products and subcellular material of cultured cells in association with project 0002.